A new study from the University of Washington and Washington State University shows that the risk of head injury among bicyclists increased 14 percent after the launch of bike-share programs in several major cities.

The study, which was published last week in the American Journal of Public Health, arrives a few months before Seattle's Pronto Emerald City Cycle Share program is scheduled to begin this fall. Ironically, two health care providers, Group Health Cooperative and Seattle Children's Hospital, are helping to sponsor Pronto Emerald City.

UW and WSU researchers looked at the change in head injuries before and after the implementation of bike-share programs in five cities in the United States and Canada. They also gathered similar data for five cities that did not have bike-share programs.

Of all bicycle-related injuries that occurred in bike-share cities during the study period, the proportion that were head injuries rose from 42 percent to 50 percent after bike-share programs began. No such increase was found in cities without these programs.Researchers were not able to determine, however, whether the injured people were using bikes in a bike-share program, nor whether they were wearing helmets.

Helmets have been shown to lower the risk of head and brain injury; not using a helmet can increase fatalities among people who incur a traumatic brain injury in a biking accident. Despite these findings, many bike-share programs worldwide do not offer helmets, according to the study.

Cyclists in Seattle and King County are required by law to wear helmets. Pronto will rent helmets with bicycles for an additional $2, but whether Pronto users will wear helmets remains to be seen.

From 2008 to 2012, an average of three bicyclists died in King County each year and 45 were severely injured in collisions with motor vehicles, according to Public Health – Seattle and King County.

The first 500 bikes and 50 Pronto docking stations will link the University District, South Lake Union, downtown Seattle and Capitol Hill. The program hopes eventually to expand to more Seattle neighborhoods and to the Eastside.

Annual and short-term memberships for Pronto will go on sale Aug. 25 at ProntoCycleShare.com. An annual membership will cost $85, a three-day pass $16 and a 24-hour pass $8. Helmet rentals will cost $2.

Pronto's start date is unclear. The website invites interested persons to sign up for email and "be the first to know when Pronto launches this fall."

Editor's note: This blog post is based on a press release from UW Health Sciences. After this blog was posted, UW Health Sciences issued a corrected press release noting that the researchers who did the study were unable to determine whether injured people represented by the data were riding bike-share bikes, nor whether they were wearing helmets. The blog post has been updated to reflect this.